Anti-resonant panels

ABSTRACT

Noise insulation may be provided by an anti-resonant panel that includes a base panel including a base panel core material and two base panel face sheets, where each of the two base panel face sheets is adjacent to an opposite side of the base panel core material. The anti-resonant panel further includes at least one stiffener-member positioned along the base panel in a defined area of the base panel, where the defined area is less than a full area of the base panel. The stiffener-member includes a stiffener-member core having a top surface, a bottom surface in contact with the base panel, a plurality of cells having walls that extend from the top surface to the bottom surface, and a stiffener-member face sheet that is seamlessly integrated with the walls of the plurality of cells along the top surface.

RELATED APPLICATIONS

This patent application is a continuation-in-part of co-pending U.S.patent application Ser. No. 15/840,902, filed on Dec. 13, 2017 andhaving the title of “AN ANTI-RESONANT PANEL AND METHODS OF MAKING THESAME”, which is hereby incorporated by reference in its entirety.

TECHNOLOGICAL FIELD

Example embodiments of the present disclosure relate generally to noiseinsulating materials and, more particularly, to methods and systemsproviding noise insulation using a panel.

BACKGROUND

Current technologies in noise insulation use passive noise controlapproaches such as sound absorbers, dampers, or blockers. Thesecomponents are usually either too large or too heavy, making theapproaches either inefficient for noise control or ineffective for lowfrequency noise control. Active noise control provides another noisecontrol option. However, active noise control requires wiring and power,which can make active noise control complex, costly, and/or difficult toimplement for noise control in applications where large surface areasare present, such as in motor vehicles, boats, or an aircraft (e.g.,“acreage noise control”).

SUMMARY

Noise-insulating panels are provided herein. The noise-insulating panelmay be an anti-resonant panel comprising a base panel and at least onestiffener-member positioned along the base panel in a defined area ofthe base panel, where the defined area is less than a full area of thebase panel. The stiffener-member comprises a continuous structure thatincludes a honeycomb core and a face sheet seamlessly integrated withthe honeycomb core. The stiffener-member is configured to provideanti-resonant performance to the base panel by adding stiffness to thedefined area of the base panel at a low mass density.

One embodiment described herein comprises an anti-resonant panelincluding a base panel and at least one stiffener-member. The base panelincludes a base panel core material and two base panel face sheets,where each of the two base panel face sheets are adjacent to an oppositeside of the base panel core material. The at least one stiffener-memberis positioned along the base panel in a defined area of the base panel,where the defined area is less than a full area of the base panel. Theat least one stiffener-member comprises a stiffener-member core having atop surface, a bottom surface in contact with the base panel, aplurality of cells having walls that extend from the top surface to thebottom surface, and a stiffener-member face sheet that is seamlesslyintegrated with the walls of the plurality of cells along the topsurface.

In an embodiment of the anti-resonant panel, the at least onestiffener-member provides anti-resonant performance to the base panel byadding stiffness to the defined area of the base panel at a low massdensity.

In an embodiment of the anti-resonant panel, the at least onestiffener-member comprises two or more stiffener-members, eachpositioned along the base panel in respective defined areas of the basepanel.

In an embodiment of the anti-resonant panel, the stiffener-member coreand the stiffener-member face sheet comprises Nylon.

In an embodiment of the anti-resonant panel, the cells comprisehexagonal cells.

In an embodiment of the anti-resonant panel, the stiffener-member coreincludes a perimeter wall extending from the top surface to the bottomsurface that surrounds the plurality of cells and is seamlesslyintegrated with the walls of the cells that are in contact with theperimeter wall.

In an embodiment of the anti-resonant panel, the anti-resonant panelreduces noise propagation through the anti-resonant panel at frequenciesbetween 300 Hertz to 1000 Hertz.

In an embodiment of the anti-resonant panel, the bottom surface of theat least one stiffener-member is bonded to the base panel utilizing anadhesive.

Another embodiment described herein comprises a method making ananti-resonant panel having a base panel with a base panel core materialand two base panel face sheets, where each of the two base panel facesheets adjacent to an opposite side of the base panel core material. Themethod comprises attaching at least one stiffener-member along the basepanel in a defined area of the base panel, where the defined area lessthan a full area of the base panel, and the at least onestiffener-member includes a stiffener-member core having a top surface,a bottom surface in contact with the base panel, a plurality of cellshaving walls that extend from the top surface to the bottom surface, anda stiffener-member face sheet that is seamlessly integrated with thewalls of the plurality of cells along the top surface.

In an embodiment of the method, the at least one stiffener-memberprovides anti-resonant performance to the base panel by adding stiffnessto the defined area of the base panel at a low mass density.

In an embodiment of the method, attaching the at least onestiffener-member comprises attaching two or more stiffener-members, eachpositioned along the base panel in respective defined areas of the basepanel.

In an embodiment of the method, the cells comprise hexagonal cells.

In an embodiment of the method, the stiffener-member core includes aperimeter wall extending from the top surface to the bottom surface thatsurrounds the plurality of cells and is seamlessly integrated with thewalls of the cells that are in contact with the perimeter wall.

In an embodiment of the method, the anti-resonant panel reduces noisepropagation through the anti-resonant panel at frequencies between 300Hertz to 1000 Hertz.

In an embodiment of the method, attaching the at least onestiffener-member comprises bonding the bottom surface of the at leastone stiffener-member to the base panel utilizing an adhesive.

Another embodiment described herein comprises a method making ananti-resonant panel having a base panel with a base panel core materialand two base panel face sheets, where each of the two base panel facesheets adjacent to an opposite side of the base panel core material. Themethod comprises additively forming, using a first series ofmanufacturing steps, a stiffener-member core having a top surface, abottom surface, and a plurality of cells having walls that extend fromthe top surface to the bottom surface. The method further comprisesadditively forming, using a second series of the manufacturing steps, astiffener-member face sheet on the top surface of the stiffener-membercore. The method further comprises attaching the bottom surface of thestiffener-member core to a defined area of the base panel, wherein thedefined area of the base panel is less than a full area of the basepanel.

In an embodiment of the method, the manufacturing steps compriseSelective Laser Sintering (SLS).

In an embodiment of the method, the stiffener-member core and thestiffener-member face sheet comprise Nylon.

In an embodiment of the method, the cells comprise hexagonal cells.

In an embodiment of the method, the method further comprises additivelyforming, using the first series of manufacturing steps, a perimeter wallextending from the top surface to the bottom surface that surrounds theplurality of cells and is seamlessly integrated with the walls of thecells that are in contact with the perimeter wall.

The above summary is provided merely for purposes of summarizing someexample embodiments to provide a basic understanding of some aspects ofthe disclosure. Accordingly, it will be appreciated that theabove-described embodiments are merely examples and should not beconstrued to narrow the scope or spirit of the disclosure in any way. Itwill be appreciated that the scope of the disclosure encompasses manypotential embodiments in addition to those here summarized, some ofwhich will be further described below.

BRIEF DESCRIPTION OF THE DRAWINGS

Having described certain example embodiments of the present disclosurein general terms above, reference will now be made to the accompanyingdrawings, which are not necessarily drawn to scale:

FIGS. 1A and 1B illustrate exemplary stiffener-members for anti-resonantpanels in accordance with some example embodiments described herein;

FIGS. 2A-2G illustrate exemplary configurations of stiffener-members inanti-resonant panels in accordance with some example embodimentsdescribed herein;

FIG. 3 illustrates a perimeter-type stiffener-member enhancing asandwich-type stiffener-member in accordance with some exampleembodiments described herein;

FIGS. 4A-4C illustrate exemplary methods of adjoining stiffener-membersto base panels in accordance with some example embodiments describedherein;

FIGS. 5A and 5B illustrate exemplary methods of attachingstiffener-members to base panels in accordance with some exampleembodiments described herein;

FIGS. 6A-6D illustrate exemplary base panels that make up the foundationof exemplary anti-resonant panels in accordance with some exampleembodiments described herein;

FIG. 7 illustrates the addition of exemplary inertial members toanti-resonant panels in accordance with some example embodimentsdescribed herein;

FIG. 8 illustrates exemplary reinforcing members in accordance with someexample embodiments described herein;

FIGS. 9A and 9B illustrate the addition of exemplary reinforcing membersto anti-resonant panels in accordance with some example embodimentsdescribed herein;

FIGS. 10A and 10B illustrate the addition of exemplary grounding membersto anti-resonant panels in accordance with some example embodimentsdescribed herein;

FIGS. 11A and 11B illustrate the double pane effect seen in exemplaryanti-resonant panels in accordance with some example embodimentsdescribed herein;

FIG. 12 is a flow chart for an exemplary method of providing noiseinsulation in accordance with some example embodiments described herein;

FIG. 13 is a flow chart for an exemplary method of forming ananti-resonant panel in accordance with some example embodimentsdescribed herein;

FIG. 14 illustrates exemplary areas where the anti-resonant panels maybe used in an aircraft and illustrates exemplary anti-resonant treatmentto a sidewall panel of the aircraft in accordance with some exampleembodiments described herein;

FIG. 15 illustrates the insertion loss of an exemplary anti-resonantpanel in accordance with some example embodiments described herein;

FIG. 16 illustrates the addition of exemplary inertial members toanti-resonant panels in accordance with some example embodimentsdescribed herein;

FIG. 17 illustrates the double pane effect seen in exemplaryanti-resonant panels in accordance with some example embodimentsdescribed herein;

FIG. 18 depicts exemplary shapes of stiffener-members for anti-resonatepanels in an illustrative embodiment;

FIG. 19 is a block diagram of an anti-resonant panel utilizing astiffener-member in an illustrative embodiment;

FIG. 20 depicts exemplary configurations of stiffener-members in ananti-resonant panel employed as an aircraft cabin panel in anillustrative embodiment;

FIG. 21 illustrates a transmission loss graph of a mass-law predictionand experimentally measured results in an illustrative embodiment;

FIG. 22 is an isometric view of a stiffener-member in an illustrativeembodiment;

FIG. 23 is an isometric view of the stiffener-member of FIG. 22 in anillustrative embodiment;

FIG. 24 is an isometric view of another stiffener-member in anillustrative embodiment;

FIG. 25 is a flow chart of a method of making an anti-resonant panel inan illustrative embodiment; and

FIG. 26 is a flow chart of a method of making an anti-resonant panel inanother illustrative embodiment.

DETAILED DESCRIPTION

In general, embodiments of the present disclosure provided hereininclude methods and systems for providing noise insulation, particularlynoise control for low frequencies. More specifically, noise insulationis provided by using an anti-resonance approach. Some embodiments of thepresent disclosure will now be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the disclosures are shown. Indeed, these disclosures maybe embodied in many different forms and should not be construed aslimited to the embodiments set forth herein; rather, these embodimentsare provided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

As used herein, “anti-resonant performance” refers to the soundtransmission loss resulting from reduction of structural net vibratorydisplacement. In certain embodiments described herein, this reduction ofstructural net vibratory displacement is generally obtained byreflecting the impacting sound waves off of the component. Suchreflection may be obtained with the disclosed materials. For example,the addition of a stiffener-member as described herein to a base panelas described herein may provide anti-resonant performance to the panelmaking the panel an anti-resonant panel.

The term “mass density” refers to the amount of matter per volume.

The term “hollowed portion” refers to a hole or vacancy of material in adefined area of the respective component such that the hollowed portionlacks the material otherwise continuous in the component. The hollowedportion may be created by removing an interior portion of the componentand be defined by an inner wall of the component. As used herein,“defined area” is generally in reference to anti-resonant units orportions of the anti-resonant panel. That is, the anti-resonant panelmay be divided into defined areas or portions. Stiffener-members maycover all or part of the defined areas. Additional components such asinertial members may be added to the defined areas and reinforcingmembers and/or grounding members may be added to defined areas,particularly along the perimeter forming the defined areas.

As used herein, “acoustic boundary” refers to a limit, generally imposedby a physical component, creating a defined acoustic transmission pathwhere sound travels differently (with regards to speed, path,transmission efficiency etc.) compared to the adjoining space. As usedherein, various components may be incorporated into the anti-resonantpanels to create acoustic boundaries allowing for more control of noisepropagation when contacting the panel. The acoustic boundaries may be inline with the perimeter of the defined area.

Overview

Provided herein are systems, devices, panels, and methods for providingnoise control, in particular by reflecting and/or blocking noise. Noiseinsulation may be provided, for example, by noise insulating panels thatinclude stiffener-members that impart anti-resonance to the panel, whichare then referred to as anti-resonant panels. The resultinganti-resonant panels may reduce the external acoustic energy passingthrough the panel, thereby providing improved noise insulation. Theanti-resonant panels include a base panel and stiffener-membersdistributed along the base panel. The anti-resonant panel may enableanti-resonance frequencies with locally out-of-phase vibration modes topassively neutralize the sound radiation through the panel and into anyenclosed structure. In conventional enclosed structures, such asaircraft cabins, cars, boats, etc., the complex geometry, largedimension, and existing attached components, such as windows, may imposesignificant challenges in structural vibration management for noisecontrol. However, the anti-resonant design of the base panels combinedwith the stiffener-members may allow for acreage noise control for suchenclosed structures. The lightweight nature and high bending stiffnessof the anti-resonant panels may provide anti-resonant based noisecontrol or anti-resonant performance. The anti-resonant panels mayachieve high sound transmission loss over a wide frequency range,particularly in the low frequency regime of hundreds to a thousand Hertz(Hz), outperforming conventional added-mass and damping approaches inthe same frequency range. Benefiting from existing components, such asattached windows or nearby frames, inertial members may be incorporatedinto the anti-resonant panels to further tune the anti-resonant design.

The anti-resonant panels may also improve double-leaf noise insulationby interacting with nearby structures, such as the fuselage skin of anaircraft. The anti-resonant panels may provide a lightweight, compact,practical, and economic solution to providing targeted noise control tostructures, such as aircraft cabins and other enclosed structures wherenoise control is of concern. The anti-resonant panels may beparticularly beneficial for areas where contoured panels are needed, assuch were previously difficult to control acoustically. Theanti-resonant panels, with the distinct stiffener-members distributedalong the base panels in defined areas, may be able to conform to thedesired shape while still achieving the anti-resonant performance of theanti-resonant panels. In some embodiments, the anti-resonant panels mayprovide lightweight noise blocking barriers for structures such asaircraft cabins and improve upon existing panels (e.g., trim panels ofboats, vehicles, or aircraft) particularly those of large dimension(e.g., acreage noise control) with conformal as well as asymmetricgeometry and may work with other components of the structure, such ascabin windows, to control noise propagation.

The anti-resonant panels may replace simple to complex panels. Ascompared to existing noise-insulating panels, the anti-resonant panelsmay have reduced manufacturing costs with simpler manufacturingtechniques, enable stiffness control, and generally provide a panel withreduced mass compared to existing noise-insulating panels. Inparticular, previous technologies use passive noise control approachessuch as sound absorbers, dampers, or blockers. These components areusually either too large or too heavy, especially for low frequencynoise control. Active noise control may provide another noise controloption. However, active noise control typically requires wiring andpower requirements making the option complex, costly, and hard toimplement for acreage noise control applications.

Indeed, there has been a long-felt need for lightweight acousticattenuation, particularly inside enclosed cabins (e.g., cabins in cars,aircraft, boats, trains, etc.). State of the art noise control used forvehicular trim panel routinely involves recycled noise controlmechanisms, such as Helmholtz-style absorption, constrained layerdamping, mass-loading, fibrous-type batting for acoustic absorption, orcombinations thereof. Generally speaking, noise above 1000 Hz may bedealt with using these approaches. However, there exists a need forlightweight noise control in the lower-frequency range, e.g., below 1000Hz.

Trim panels used in vehicles requiring lightweight design typicallyinclude a sandwich-type design, which enables a relatively durableboundary wall that forms the interior walls of the enclosed cabin, yetoffers a relatively lightweight solution. Such panels and any panel thatis lightweight, relatively stiff, and relatively large in area makes fora sound radiator. These trim panels also make up much of the interiorsurface of the vehicle, which make the trim panels a prime influence onthe acoustic properties inside the vehicle. These trim panels canproduce global vibratory modes that dominate the noise frequency range,especially below 1000 Hz, and have been difficult to mitigate withoutmass loading the trim panels, which, if implemented, results in asignificant mass penalty and corresponding decreased fuel efficiency.

Provided herein is a passive noise control technology with advantages oflightweight, compactness, high noise reduction, and environmentalrobustness. The anti-resonant panels provide a conformal soundinsulating panel with high noise reduction that may provide alightweight noise control solution for high quality travellingexperience. For instance, the anti-resonant panels can be used as trimpanels in an aircraft cabin, as partitions, bulkhead, sidewalls, andfloors for various airplane models, to reduce noise propagation into andbetween chambers. In addition, the anti-resonant panels may be used as,for example, housings or partitions, in various commercial products thatcontain noisy components (e.g., motors, pumps, compressors,transmissions, transformers, ducts, etc.) including appliances,grinders, blenders, microwave ovens, sump pumps, etc. The anti-resonantpanels may be suitable for a variety of applications, such as anyapplication where noise control is desired, without deviating from theintent of the present disclosure.

The anti-resonant panels may employ a sound-reflection mechanism, usinganti-resonance to reflect a tuned bandwidth of sound energy from thepanel. The disclosed mechanism may involve a slight mass penalty ascompared to unmodified panels, although the mass penalty involved may besignificantly less than what would otherwise be used to create similartransmission loss performance based on mass law predictions. Theanti-resonant panels' transmission loss performance may extend beyondthe panel's predicted mass-law sound-attenuation limit within the lowfrequency range of interest by modifying the global panel vibratorymodes. In some embodiments, other components, such as one or moreinertial members, grounding members, and reinforcing members may beadded to modify the global panel vibratory modes.

The anti-resonant panel may be particularly effective in the lowfrequency range (e.g., about 300 Hz to about 1000 Hz) without adding asignificant amount of mass. The anti-resonant bandwidth may be tailoredto meet a target range of problem noise frequencies associated with theunmodified base panel as disclosed herein. Furthermore, currentengineered trim panel designs are inherently complex in shape, asarchitectural designs and features are desired in most passengeraircraft and vehicles. Such complexity can make the implementation of ananti-resonant design difficult. Provided herein are panels withanti-resonant performance using a diverse range of panel materials,shapes, sizes, and orientations to enhance the versatility of the panelsfor use in various applications. The noise control mechanism may have anadded benefit of being relatively unaffected by temperature, humidity,and pressure changes, which further makes the panels suitable forvehicles that routinely experience fluctuations in environmentalconditions, such as aircraft, trains, and automobiles.

The anti-resonant panels may improve upon existing tunablesandwich-structured acoustic barriers by implementing anti-resonancecontrol, particularly for geometrically complex panels with asymmetricgeometry and of a large dimension. Further, the anti-resonant panels mayenhance double-pane soundproofing in terms of wide bandwidth and noisereduction by interacting with nearby panels.

In some embodiments, pre-qualified materials may be used for theanti-resonant panels to create a noise control or acoustic blockingstructure over an acreage area for noise management.

Having described example embodiments at a high level, the design of thevarious configurations performing various example operations is providedbelow.

Provided herein are anti-resonant panels with anti-resonance soundblocking performance to provide noise insulation. In some embodiments,the technology may be passive in nature, not relying on electronics oractuation for the sound blocking performance. The anti-resonant panelsmay include sandwich-type base panels, which are lightweight and stiff;can be manufactured in various sizes, thickness, and materials, such aspre-qualified aviation materials; and can be mounted in various ways.The anti-resonant panels also include a stiffener-member with the basepanel. Without intending to be bound by theory, the stiffener-memberprovides localized stiffness to specific areas (“defined areas”) of thebase panel resulting in anti-resonant performance of the resultingpanel.

The anti-resonant panels may have the capability to block low frequencysound and may use preexisting composite materials that may already befully qualified for use in vehicles, such as aircraft. The mechanicalproperties of the anti-resonant panels may provide improved soundblocking performance for noise insulation. The anti-resonant panels maybe used in any application where lightweight, strong paneling isdesired, such as fuel-efficient vehicles and the like.

FIG. 1A illustrates exemplary shapes for stiffener-members 108. FIG. 1Billustrates additional exemplary shapes for stiffener-members 108. Thestiffener-members 108 may include hollowed portions 124, such as shownin FIG. 1B, such that the stiffness and surface density of the finaldesign of the stiffener-member 108 are altered, ultimately altering thestiffness-to-mass ratio of the stiffener-member 108. Thestiffener-member 108 may include an interior wall 122 defining ahollowed portion 124 in the stiffener-member 108. The hollowed portions124 may cut vertically through the stiffener-member 108 (e.g., througheach of the stiffener-member core material 114 and stiffener-member facesheets 116, 117 of the stiffener-member 108 (shown in FIGS. 2A-2G)).Such hollowing of the stiffener-members 108 may reduce the mass of thestiffener members 108 without significantly reducing the stiffness ofthe stiffener members 108. That is, the stiffener members 108 are stillstiff enough to manipulate the dynamics of the anti-resonant panels 100while not adding significant mass to the anti-resonant panels 100.Variations on this manipulation of the stiffener-members 108 may be usedto obtain the desired anti-resonant performance.

FIGS. 2A-2G provide various exemplary configurations ofstiffener-members 108 on base panels 102. To provide the anti-resonanceeffect, one or more stiffener-members 108 can be used with the basepanel 102. The stiffener-members 108 control the global vibratory modesand enable the anti-resonant design. Stiffener-members 108 can encompassany shape, number, orientation, or location as needed to enableanti-resonant performance of the resulting anti-resonant panels 100. Forexample, in some embodiments, the stiffener-members 108 may be about 10%to about 30% of the total mass of the anti-resonant panel 100, such asabout 15% to about 25% of the total mass of the anti-resonant panel 100,such as about 20% or less of the total mass of the anti-resonant panel100.

The stiffener-members 108 may cover less than 40% of the total surfacearea of the anti-resonant panel 100 (e.g., less than 40% of the totalsurface area of the side of the anti-resonant panel 100 on which thestiffener-member(s) 108 are placed), such as less than 35% of the totalsurface area of the anti-resonant panel 100 (e.g., less than 35% of thetotal surface area of the side of the anti-resonant panel 100 on whichthe stiffener-member(s) 108 are placed), such as less than 30% of thetotal surface area of the anti-resonant panel 100 (e.g., less than 30%of the total surface area of the side of the anti-resonant panel 100 onwhich the stiffener-member(s) 108 are placed), such as less than 25% ofthe total surface area of the anti-resonant panel 100 (e.g., less than25% of the total surface area of the side of the anti-resonant panel 100on which the stiffener-member(s) 108 are placed), such as less than 20%of the total surface area of the anti-resonant panel 100 (e.g., lessthan 20% of the total surface area of the side of the anti-resonantpanel 100 on which the stiffener-member(s) 108 are placed). In someembodiments, the stiffener-member 108 may be disposed along less than25% of a total surface area of the base panel 102 and a mass of thestiffener-member 108 may be about 20% or less of a total mass of theanti-resonant panel 100. With such low coverage of the total surfacearea of the base panel 102 (e.g., less than 40% of the total surfacearea of the anti-resonant panel 100) and low mass addition to the totalmass of the anti-resonant panel 100 (e.g., less than 30% of the totalmass of the anti-resonant panel 100), the stiffener-member 108 is ableto increase the stiffness of the base panel 102 without significantlyimpacting the mass of the base panel 102 and provide control of theanti-resonant performance due to the discrete nature of thestiffener-members 108. The density and thickness of thestiffener-members 108 may vary based on the desired anti-resonantperformance. The stiffener-members 108 will generally have a low massdensity and high stiffness.

The various configurations presented in FIGS. 2A-2G are a few examplesof configurations that may alter the stiffness and mass-densityproperties of the resulting anti-resonant panel 100. Thestiffener-members 108 of the present disclosure are not limited to thoseshown in FIGS. 2A-2G and may include a variety of materials in a varietyof configurations without deviating from the intent and scope of thepresent disclosure. For instance, the stiffener-members 108 can be acombination of the following materials and/or other materials anddesigns that provide the desired lightweight but stiff combination andimpart an acoustic boundary 132 to the base panel 102. For instance, thestiffener-member face sheets 116, 117 may be lightweight, strongmaterial such as carbon fiber, fiberglass, or combinations thereof. Thestiffener-member core material 114 may comprise foam (e.g., polyethyleneterephthalate (PET) foam), be of a honeycomb construction (e.g., aramidhoneycomb construction), otherwise have a porous structure, orcombinations thereof. In some embodiments, the stiffener-member corematerial 114 may comprise PET foam, aramid honeycomb construction, orcombinations thereof.

The stiffener-member face sheets 116, 117 may comprise carbon-fiber,fiberglass, combinations thereof, or other similar materials. In someembodiments, the stiffener-member face sheets 116, 117 may comprisecarbon fiber, fiberglass, a fiber composite, or combinations thereof.Metal (e.g., aluminum) struts, trusses, or porous structures may be usedto impart stiffness while not significantly increasing mass. Twodifferent stiffener-member core materials 114 are shown in FIGS. 2A-2G.As the stiffener-members 108 are discrete, concentrated areas along thebase panel 102, the materials may have a higher modulus than materialsthat would typically be used for construction of a base panel 102. Inaddition, materials that may be of a flammability concern in largeareas, may be used in the stiffener-members 108 as such are generallysmaller, more concentrated, discrete areas along the base panel 102rather than the full length/width of the base panel 102.

As shown in FIGS. 2A-2G, multiple stiffener-member face sheets 116and/or 117 may be used to form the stiffener-member 108 and/or multiplestiffener-member core materials 114 may be used to form thestiffener-member 108. In some embodiments, multiple stiffener-members108 may be disposed on a base panel 102. For instance, the anti-resonantpanel 100 of FIG. 2E includes a first stiffener-member 108 a and asecond stiffener-member 108 b, each in respective defined areas 110 a,110 b on the base panel 102. The first and second stiffener-members 108a, 108 b are shown in FIG. 2E as having the same compositions, however,the compositions of the first and second stiffener-members 108 a, 108 bmay be the same or different and more than two stiffener-members 108 maybe incorporated on/into the base panel 102. Variations on the number andcombination of these materials may be used to achieve the desiredanti-resonant performance.

In some embodiments, the anti-resonant panels 100 may includestiffener-members 108 disposed on one of the two base panel face sheets106, 107. In some embodiments, the anti-resonant panels 100 may includestiffener-members 108 disposed between the two base panel face sheets106, 107 and adjacent to the base panel core material 104. FIGS. 2A-2Eillustrate stiffener-members 108 applied to the base panel face sheets106, 107 while FIGS. 2F and 2G illustrate stiffener-members 108 appliedto the interior of the base panel 102 and covered by the base panel facesheets 106, 107. In particular, in FIGS. 2F and 2G, thestiffener-members 108 replace a portion of the base panel core material104. As shown in FIG. 2G, a first stiffener-member face sheet 116 may beapplied externally to the base panel face sheet 106 using an adhesive(attachment mechanism 146). Such placement of the stiffener-member facesheet 116 may further increase the bending stiffness of the defined area110 in which the stiffener-member 108 is disposed.

When being applied to the interior of the base panel 102, thestiffener-member 108 may include stiffener-member core material 114 andone or more stiffener-member face sheets 116, 117 or simplystiffener-member core material 114 without one or more stiffener-memberface sheets 116, 117. Stiffener-member face sheets 116, 117 may beapplied to the interior of the base panel 102 (e.g., under one or morebase panel face sheets 106, 107 (shown in FIGS. 6A-6D)) and/or appliedto the exterior of the base panel 102 (e.g., over one or more base panelface sheets 106, 107).

The stiffener-members 108 may be designed to provide the desired degreeof anti-resonant performance by including the stiffener-members 108 inspecific regions (e.g., defined areas 110) of base panels 102 and withspecific constructions. That is, the materials, size, shape, andconfiguration of materials for the stiffener-members 108 may be modifiedto achieve the desired anti-resonance behavior. In some embodiments, theanti-resonant panel 100 may include two or more stiffener-members 108(e.g., first and second stiffener-members 108 a and 108 b as shown inFIG. 2E) each positioned along the base panel 102 in respective definedareas 110 (e.g., first and second defined areas 110 a and 110 b as shownin FIG. 2E) of the base panel 102.

Without intending to be limited by theory, the stiffener-member 108 mayprovide an efficient acoustic boundary on the base panel 102 therebyenabling alteration of the global vibratory modes of the anti-resonantpanel 100 (that is, the vibratory modes of the whole base panel 102 suchas the first and second principal modes and the anti-resonant mode inbetween). In some embodiments, the stiffener-member 108 may have asandwich-type construction (e.g., comprising two stiffener-member facesheets 116, 117 surrounding a stiffener-member core material 114 onopposite sides of the core material 114), which may enable lightweightbut high bending stiffness resulting in a sandwich-type stiffener member108. Various other stiffener-member 108 configurations with highstiffness-to-mass ratio are discussed herein. The high stiffness-to-massratio may allow for anti-resonant performance while also allowing forhigh fuel efficiency when applied to vehicles. In some embodiments, theanti-resonant panel 100 may be configured to reduce noise propagationthrough the anti-resonant panel 100 at frequencies between about 300 Hzto about 1000 Hz. For instance, the anti-resonant panel 100 may includea stiffener-member 108 (e.g., stiffener-member 108 in FIGS. 1A-1B,2A-2G, 4A-4C, and 5A-5B) on a base panel 102 (e.g., base panel 102 inFIGS. 2A-2G, 4A-4C, 5A-5B, and 6A-6D) that may reduce noise propagationthrough the anti-resonant panel 100 at low frequencies (e.g., about 300Hz to about 1000 Hz), which are typically difficult to reduce or controlwith base panels alone.

In some embodiments, one or more stiffener-members 108 may be added toone or more base panels 102, in particular to one or more base panelface sheets 106, 107 to alter the stiffness-to-mass ratio of the basepanel 102. The anti-resonant panels 100 include a base panel 102comprising a base panel core material 104 and two base panel face sheets106, 107, each of the two base panel face sheets 106, 107 adjacent to anopposite side of the base panel core material 104; and at least onestiffener-member 108 positioned along the base panel 102 in a definedarea 110 of the base panel 102, the defined area 110 being less than afull area 112 of the base panel 102; wherein the stiffener-member 108comprises a stiffener-member core material 114 and two stiffener-memberface sheets 116, 117, each of the two stiffener-member face sheets 116,117 adjacent to an opposite side of the stiffener-member core material114, and wherein the stiffener-member 108 is configured to provideanti-resonant performance to the base panel 102. The stiffener-member108 may be configured to provide anti-resonant performance to the basepanel 102 by adding stiffness to the defined area 110 of the base panel102 at a low mass density.

For instance, as shown in FIGS. 2A-2G, 3, 4A-4C, the stiffener-member108 may provide stiffness by being constructed as a sandwich-typestiffener-member comprising at least one stiffener-member face sheet116, 117 and a stiffener-member core material 114 and being preparedwith materials described herein. In some embodiments, thestiffener-member 108 may add stiffness at a low mass density byincluding a hollowed portion 124 as shown in FIG. 1B and/or be disposedon the base panel as shown in FIG. 5A-5 b or 4A-4C. The one or morestiffener-members 108 are disposed on the exterior surface of the one ormore base panel face sheets 106, 107. In some embodiments, one or morestiffener-members 108 may be added to the interior base panel corematerial 104 and then surrounded by the base panel face sheets 106, 107.The one or more stiffener-members 108 may be applied to the base panelcore material 104 and/or used in place of the base panel core material104 in defined areas 110 of the base panel 102. One or morestiffener-members 108 may be added to defined areas 110 of the basepanel 102 to alter the stiffness-to-mass ratio of the base panel 102 atspecific points along the base panel 102. Various stiffener-member facesheets 116, 117, adhesive films or adhesive materials (collectivelyreferred to as “attachment mechanisms” 146), and stiffener-member corematerials 114 can be used to form the stiffener-members 108 and achievethe desired stiffness and specific mass properties of the finalstiffener-member 108 and the resulting anti-resonant panel 100.

The configurations described in FIGS. 1A-1B and 2A-2G are examples ofembodiments that can effectively be used as stiffener-members 108 foranti-resonant performance. Combinations of these examples as well asother configurations of the stiffener-members 108 may be used inconjunction with the base panels 102 to provide anti-resonant panels 100with the improved anti-resonant performance.

In some embodiments, as shown in FIG. 3, stiffener-members 108 caninclude a perimeter-type stiffener-member 118 that is lightweight andfurther increases the stiffness of the anti-resonant panel 100. Theanti-resonant panel 100 may include a perimeter-type stiffener-member118 disposed along one or more edges 120 of the stiffener-member 108.For instance, in some embodiments, perimeter-type stiffener-members 118may be included to reinforce a stiffener-member 108, such as asandwich-type stiffener-member 108 (see e.g., FIG. 3), or may be usedalone as the stiffener-member 108. The perimeter-type stiffener member118 is particularly effective in performance when disposed along theperimeter of a sandwich-type stiffener-member 108 to further improve theanti-resonant performance of the anti-resonant panel 100. For instance,FIG. 3 shows a lightweight perimeter-type stiffener member 118 enhancingthe sandwich-type stiffener-member 108, which then engages to asandwich-type base panel 102.

As shown in FIG. 3, the perimeter-type stiffener member 118 may be havea Z-shaped cross-section (e.g., two parallel horizontal portions areconnected by a vertical portion, the two parallel horizontal portionsindependently connected to the vertical portion at opposite ends of thehorizontal portions, forming a Z-shaped cross section) and extend alongone or more sides or edges 120 of the sandwich-type stiffener-member108. For instance, in the embodiment illustrated in FIG. 3, theperimeter-type stiffener member 118 traces the perimeter of thesandwich-type stiffener-member 108 along three edges 120 of thesandwich-type stiffener-member 108. However, the perimeter-typestiffener member 118 may trace one, two, or all edges 120 of asandwich-type stiffener-member 108. The stiffness of the anti-resonantpanel 100 is particularly increased when the perimeter-type stiffenermember 118 connects three or more edges 120 enclosing a perimeter asshown in FIG. 3. The perimeter-type stiffener member 118 may have across-section that is I-shaped (e.g., two parallel horizontal portionsare connected by a vertical portion, the two parallel horizontalportions centered on top and on the bottom of the vertical portion,forming an I-shaped cross-section), L-shaped (e.g., a single horizontalportion is attached on the bottom of a single vertical portion formingan L-shaped cross-section), Z-shaped, T-shape (e.g., a single horizontalportion is attached on top of a single vertical portion forming aT-shaped cross section), etc. or may have any other suitableconfiguration to provide a lightweight stiffener member 108 to thesandwich-type base panel 102.

In some embodiments, the materials for the stiffener-members 108 may bepre-qualified materials already suited for the aerospace or automotiveindustry. In some embodiments, the same materials that make up the basepanel 102 may be used for the stiffener-members 108, though differing inconfiguration, size, and thickness to achieve the desired anti-resonantperformance.

The anti-resonant performance of the anti-resonant panels 100 can befurther improved by maximizing the bonding rigidity of thestiffener-member 108 to the base panel 102. The engagement of thestiffener-member 108 to the base panel 102 may be as complete aspossible, especially along the perimeter or edges 120 of thestiffener-member 108. FIGS. 4A-4C provide exemplary methods of adjoiningstiffener-members 108 to base panels 102. FIG. 4A provides ahigh-stiffness, highly-conformal stiffener-member 108 formed in a moldto fit the shape of the base panel 102. As used herein, “conformal”refers to the shaping of the item to closely fit adjacent components.For instance, with regards to the conformal stiffener-member 108, thesurface of the stiffener-member 108 (e.g., one of the stiffener-memberface sheets 116, 117) is immediately adjacent to the base panel 102 andfollows the curvature of the base panel 102. The stiffener-member 108geometry is traced and cut away to form the stiffener-member 108 for theanti-resonant panel 100.

Particularly beneficial for complex stiffener-members 108, thestiffener-member 108 may be pre-fabricated as stiffener-member panelstock 150 in a mold. From this stiffener-member panel stock 150, aspecific area predetermined to produce the desired anti-resonantperformance is cut out (stiffener-member cut-out 152) and superimposedas the stiffener-member 108 to an existing base panel 102. This methodis especially practical if specific defined areas 110 requiring thestiffener-members 108 are complex or highly contoured, as shown in FIG.4A. This treatment allows for high bonding engagement of thestiffener-member 108 to the base panel 102, which can increase theeffective stiffness of the resulting anti-resonant panel 100.

The stiffener-member 108 may be joined to the base panel 102 by othermethods. FIG. 4B shows an exemplary process of forming thestiffener-member 108 on the base panel 102. In particular, FIG. 4Billustrates an exemplary method of stiffener-member 108 formation by alayup process, in which the constituents (in this embodiment, thestiffener-member face sheets 116, 117, the attachment mechanisms 146,and the stiffener-member core material 114) that make up thestiffener-member 108 are flat, but flexible, allowing the constituentsto take on the surface contours of the base panel 102 (including thebase panel face sheets 106, 107 and base panel core material 104) duringthe layup process. The stiffener-member 108 and base panel 102 are thenbonded together to form the anti-resonant panel 100. An autoclave may beused to achieve higher bonding pressures once the setup has beenestablished, or sandbags may be applied over the attachment to aid inbonding. The method shown in FIG. 4B may be more cost effective andefficient than other methods.

FIG. 4C illustrates another exemplary method of adjoiningstiffener-members 108 to base panels 102. In particular, in theembodiment illustrated in FIG. 4C, a stiffener-member 108 may beprepared, for example, by cutting out the stiffener-member 108 fromstiffener-member panel stock 150 (see e.g., FIG. 4A), building up thestiffener-member with pre-cut constituents of the stiffener-member (seee.g., FIG. 4B), the like, or combinations thereof. The stiffener-member108 includes a stiffener-member core material 114 and stiffener-memberface sheets 116, 117. A portion of the base panel core material 104 maybe removed to allow for the insertion of the stiffener-member 108. Basepanel face sheets 106, 107 may then be applied to the base panel corematerial 104 and stiffener-member 108 forming the anti-resonant panel100. In such embodiment, the stiffener-member 108 is incorporated intothe base panel 102 thereby imparting the stiffer properties of thestiffener-member 108 to the base panel 102 and providing a resultinganti-resonant panel 100 with a flush or regular surface. In someembodiments, the stiffener-member 108 may be incorporated into the basepanel 102 by adhering the stiffener-member 108 to the base panel corematerial 104 and then applying base panel face sheets 106, 107 over boththe stiffener-member 108 and the base panel core material 104 withoutcutting out a portion of the base panel core material 104. Variations onthese methods may be used without deviating from the intent of thepresent disclosure and other methods can be used to achieve similarresults based on available supplies or capital.

Once a design for the stiffener-member 108 is designated, thestiffener-member 108 can be attached to the base panel 102 by severalmeans, with some examples shown in FIGS. 5A and 5B. In particular, FIGS.5A and 5B provide exemplary processes for attaching a stiffener-member108 to a base panel 102. In FIG. 5A, the stiffener-member 108 ispre-fabricated and attached by way of mechanical fasteners (e.g.,attachment mechanism 146) to the base panel 102. FIG. 5A also shows across-section of the resulting anti-resonant panel 100. In FIG. 5B, thestiffener-member 108 is pre-fabricated and attached by way of adhesivefilm (e.g., attachment mechanism 146) and an auto-clave layup to thebase panel 102. FIG. 5B also shows a cross-section of the resultinganti-resonant panel 100 illustrating the direct attachment of thestiffener-member 108 to the base panel 102. Variations in bondingtechniques can be used, such as hot press, vacuum bagging, sand-bagging,the like, and combinations thereof and various materials can be usedsuch as screws, adhesive, adhesive film, rivet, and combinationsthereof. For instance, in one embodiment, a rigid foam-forming adhesivemay be used to ensure gaps are securely filled and adhered between thetwo interfaces (e.g., between the stiffener-member 108 (e.g., one ormore stiffener-member face sheets) and the base panel 102). Variousmethods in attaching the components may be used without deviating fromthe intent and scope of the present disclosure. For instance, in someembodiments, it may be desirable to combine one or more fabrication andadhesion techniques from FIGS. 4A-4C and FIGS. 5A-5B.

FIGS. 6A-6D are exemplary base panels 102, particularly sandwich-typebase panels 102, which may be used for the anti-resonant panels 100 asdescribed herein. Each of the base panels 102 depicted in FIGS. 6A-6Dinclude base panel face sheets 106, 107 and base panel core material 104making the panels sandwich-type base panels 102. While the embodimentsillustrated in FIGS. 6A-6D use the same base panel face sheets 106, 107for either side of the base panel core material 104, the base panel facesheets 106, 107 may vary within an anti-resonant panel 100 (that is,different types (i.e., materials) of base panel face sheets 106, 107 maybe used on opposite sides of the base panel core material 104 and/oralong the same side of the base panel core material 104). In addition,while the embodiments illustrated in FIGS. 6A-6D use the same base panelcore material 104 for the length and width of the base panel 102, thebase panel core material 104 may vary within an anti-resonant panel 100.

FIG. 6A is a flat sandwich-type base panel 102 with carbon-fiber basepanel face sheets 106, 107 surrounding an aramid honeycomb base panelcore material 104. FIG. 6B is a contoured sandwich-type base panel 102of the same materials used in FIG. 6A with a thicker base panel corematerial 104 and contoured shape (base panel face sheets 106, 107 andbase panel core material 104). FIG. 6C is a flat sandwich-type compositebase panel 102 with fiberglass base panel face sheets 106, 107surrounding an aramid honeycomb base panel core material 104 within-plane contoured cutouts. FIG. 6D is a sandwich-type base panel 102composed of thin aluminum base panel face sheets 106, 107 surrounding aPET foam base panel core material 104. The thickness of the base panel102, particularly the base panel core material 104, in FIG. 6D is variedalong the base panel 102 to create a contoured portion 160 of the basepanel 102. The contoured base panels 102 may include a variety ofcurvature and angles to provide the desired shape and configuration. Forinstance, the base panel 102 may be contoured in various portions of thebase panel 102 to specifically fit the desired location in the wall inwhich the anti-resonant panel 100 is to be used and/or to achieve thedesired noise-insulating performance of the anti-resonant panel 100.

The base panels 102 of the present disclosure are not limited to thoseshown in FIGS. 6A-6D and may include a variety of materials in a varietyof configurations without deviating from the intent and scope of thepresent disclosure. For instance, the base panels 102 in theanti-resonant panels 100 can be a combination of these materials and/orother materials and designs that create lightweight and stiff panelingwith anti-resonant performance.

As panel size increases, the anti-resonant sound-blocking performancemay become vulnerable to the low-frequency range of audible frequencies,e.g., 300 Hz-1000 Hz, as the effective acoustic boundaries expand. Thisbehavior is usually governed by the creation of undesirablevibro-acoustic modes having characteristic geometric patternssuper-positioned on the panel at distinct frequencies. Mitigation ofthese modes can be addressed by modifying specific locations on thepanel, as determined from various tools used in acoustic measurement andmodeling, with the use of the stiffener-members 108. Additionalcomponents may be added to the anti-resonant panels 100 to provideimproved performance. For example, inertial members 126 (see e.g., FIG.7), reinforcing members 128 (see e.g., FIGS. 8A and 8B), groundingmembers 134 (see e.g., FIGS. 9A and 9B), and combinations thereof may beadded to strategic panel locations to further improve the anti-resonanceof the anti-resonant panels 100. These treatments can further tune theanti-resonant performance of the anti-resonant panels 100. In someembodiments, the additional components may provide a wider bandwidth oftransmission loss, may shift the bandwidth to higher frequencies, orcombinations thereof. As an added benefit, inertial members 126 and/orgrounding members 134 along the defined acoustic boundary 132 of thesub-divided anti-resonant panel 100 are effective to increase thequality factor (Q) of the anti-resonant performance, increasing thesound-blocking performance even further.

Inertial members 126 are generally discrete high-density componentsadded to the anti-resonant panel 100 to provide a relatively smallamount of mass in a specific portion of the anti-resonant panels 100.The anti-resonant panel 100 may include at least one inertial member126. The inertial member 126 is configured to provide a mass increaseover the defined area 110 of the anti-resonant panel 100. For instance,as shown in FIG. 7, one or more inertial members 126 may be added to theanti-resonant panel 100. In such an instances, the inertial members 126include material(s) and have a geometry to increase the mass density ofthe anti-resonant panel 100 at the particular location of the inertialmember 126. That is, the inertial members 126 provide high mass densityin a small diameter (e.g., the inertial members 126 generally have asmaller diameter than the diameter of the stiffener-members 108, buthave a higher mass density than the mass density of thestiffener-members 108). In some embodiments, the inertial members 126may have a mass density of about 5, 10, or more times the mass densityof the stiffener-members 108 and are generally too small in size toprovide stiffness to the anti-resonant panels 100 (e.g., the inertialmembers 126 have a smaller diameter than the diameter of thestiffener-members 108 and do not provide the stiffness that thestiffener-members 108 are able to provide). The inertial member 126 mayhave a mass density of about 10 times a mass density of thestiffener-member 108. The mass density may be such that a high increasein mass is provided over a small diameter to effectively increase themass at that location without significantly increasing the total mass ofthe anti-resonant panel 100. In comparison, the stiffener-member 108 mayincrease the stiffness of the panel without significantly increasing themass of the panel.

For instance, the density of the inertial members 126 may be about 0.5kg/m³ to about 30 kg/m³, such as about 1 kg/m³ to about 20 kg/m³. Theinertial members 126 provide concentrated masses at a particularlocation that shift local modes out of the target frequency range orsuppress the local vibrations (e.g., FIG. 15). In some embodiments,there is a diminishing return in transmission loss gained as massincreases with the incorporation of inertial members 126. Thus, theaddition of inertial members 126 is a balance between the increase inmass and the desired transmission loss in the desired frequency range.The addition of the inertial members 126 as point-masses can helpmaintain anti-resonance with minimal mass penalty. The inertial members126 may include solid aluminum, rubber, tungsten, ceramic, or acombination thereof as such materials provide a relatively high massdensity without significantly increasing the mass of the panel.

The inertial members 126 provided herein may be of any suitable geometryand material to provide a relatively small amount of mass to help tunethe acoustic properties of the anti-resonant panels 100. The inertialmembers 126 may be fastened using attachment mechanisms (e.g.,attachment mechanisms 146), such as mechanical fasteners, adhesives,other methods noted herein, the like, or combinations thereof. Althoughthe inertial members 126 can embody any shape, the inertial members 126are constrained to being effective as point-masses irrelevant of shape.

FIG. 7 illustrates the incorporation of exemplary inertial members 126to an anti-resonant panel 100. FIG. 7 illustrates both inertial members126 and a stiffener-member 108 (one stiffener-member face sheet 116 andthe stiffener-member core material 114 are shown) on a sandwich-typebase panel 102 (including base panel face sheets 106, 107 and base panelcore material 104) forming an anti-resonant panel 100.

Another treatment to preserve the anti-resonant performance is the useof reinforcing members 128 to reinforce regions of the anti-resonantpanel 100 (see e.g., FIGS. 9A and 9B). The anti-resonant panel 100 mayinclude a reinforcing member 128. The reinforcing member 128 is disposedalong a perimeter 130 of the defined area 110 of the base panel 102 anddefines an acoustic boundary 132 for the defined area 110 of the basepanel 102. The reinforcing members 128 divide the anti-resonant panels100 acoustically by imposing a barrier at the particular location alongthe anti-resonant panel 100, forming acoustic boundaries 132. Thereinforcing members 128 can help improve control of the overall acousticperformance of the anti-resonant panel 100 with such division. Thereinforcing members 128 can be placed in any orientation and any numberof the reinforcing members 128 may be used in positions suitable toimprove the anti-resonant performance. The reinforcing members 128 mayhelp delineate acoustic boundaries 132 of the anti-resonant panel 100,in particular non-planar or contoured anti-resonant panel 100.

FIG. 8 illustrates cross-sectional profiles of exemplary reinforcingmembers 128 that can be used for the reinforcement of variousanti-resonant panels 100. Solid construction-type and sandwich-typereinforcing members 128 are shown. The cross-sectional geometry of thereinforcing members 128 can embody several types commonly used in theindustry (I-shaped, L-shaped, Z-shaped, T-shaped, etc.), as well asnewer or more complex cross-sectional geometries that maximize thestiffness-to-mass ratio. The length and size of the reinforcing members128 may be designed to achieve particular anti-resonant performance.

The reinforcing members 128 can be made out of any type of material, canbe a composite material, have a sandwich-type construction, the like, orcombinations thereof suitable to provide a lightweight component with ahigh bending stiffness (e.g., comparable to the stiffener-member 108).The attachment mechanism 146 for the reinforcing members 128 can bethose used in attaching the stiffener-members 108 described earlier, orother mechanisms favorable for constraining vibratory movement with aminimal mass-density penalty over the footprint of the reinforcingmember 128. The reinforcing members 128 may include various materials,such as pre-approved composite materials, such as those found in theconstruction of base panels 102. The reinforcing members 128 can beconfigured in perimeter configurations similar to the perimeter-typestiffener-members 118 so long as the reinforcing members 128 enhance thepartition of the anti-resonant panels 100 creating acoustic boundaries132 for higher efficiency anti-resonant panels 100. The reinforcingmembers 128 are generally elongate members (length greater than width).

FIG. 9A illustrates exemplary reinforcing members 128 that are able tofurther improve the anti-resonance control for the anti-resonant panels100 and boost transmission loss. More specifically, FIG. 9A illustratesa profile view of a system 200 including reinforcing members 128 used tohorizontally reinforce anti-resonant panels 100 employed as an aircraftcabin panel 202. FIG. 9B illustrates a system 200 including verticalsandwich-type reinforcing members 128 to reinforce portions of theanti-resonant panels 100 employed as an aircraft cabin panel 202.Various configurations of the reinforcing members 128 may be used toimprove the anti-resonant performance of the anti-resonant panels.

Periodically mounting the anti-resonant panels 100 to a structure 136,such as a fuselage skin 137 (see e.g., FIG. 14) or a window 224 (seee.g., FIGS. 9A and 9B), may be used to further redefine the acousticboundaries 132, favoring anti-resonant performance (see e.g., FIGS. 10Aand 10B).

Referring to FIGS. 10A and 10B, grounding members 134 can be used toanchor the anti-resonant panels 100 to other components of the structure136, such as a fuselage skin 137 or a window 224. The anti-resonantpanel 100 may include a grounding member 134. The grounding member 134is configured to anchor the anti-resonant panel 100 to a structure 136,such as a fuselage skin 137 or a window 224, and define an acousticboundary 132 for the defined area 110 of the base panel 102. Groundingmembers 134 may take advantage of existing parts of the structure 136(e.g., those that have high mass, such as a fuselage skin 137 or awindow 224) to provide the anti-resonant panels 100 more stablevibratory acoustic boundaries 132. The grounding members 134 can helpisolate and control vibrations and improve the anti-resonant performanceof the anti-resonant panel 100.

In embodiments where the anti-resonant panels 100 are used in aircraft(see e.g., aircraft 145 in FIG. 13), several locations along thefuselage skin 137 can be used as anchoring points to attach groundingmembers 134 to the anti-resonant panels 100 to further improveanti-resonant performance. Convenient anchoring locations on portions ofthe fuselage skin 137 can be used, such as the windows 224, stringers,circumferential frame portions, or similar points nearby. The selectionof anchoring points for attaching grounding members 134 to theanti-resonant panels 100 can include nearby components as well that areanchored to the fuselage skin 137 to reduce the additional mass offasteners or parts required to achieve effective anchoring performance.

FIG. 10A illustrates a profile view of an exemplary system 200 includingthe anti-resonant panels 100 and the adjacent fuselage skin 137 and FIG.10B illustrates a back-facing view of an exemplary system 200 includingof anti-resonant panels 100 and the adjacent fuselage skin 137.Exemplary grounding members 134 are illustrated. The grounding members134 are attached at specific portions of the anti-resonant panel 100 toform suitable acoustic boundaries 132 favorable to anti-resonantperformance. The grounding members 134 can include brackets, anchoringbolts, other fasteners, or combinations thereof that have the capacityto anchor the portion of anti-resonant panel 100 on which the groundingmembers 134 are attached and the adjoining fuselage skin 137. Further,damping can be added along the anchoring grounding member 134 to reduceinduced vibration from the fuselage skin 137 to the anti-resonant panel100 at the attachment point or area.

In aircraft (see e.g., aircraft 145 in FIG. 14), while the aircraft trimpanels 154 define the side walls of the cabin of the vehicle, thefuselage skin 137 located behind the trim panel 154 acts as the exteriorvehicle body. The gap between these two components (the trim panel 154and the fuselage skin 137) can be acoustically exploited, in which theoverall acoustic attenuation can be increased over a wide bandwidth.This architecture may be referred to as a double-pane architecture. Thetrim panels 154 may be replaced with one or more anti-resonant panels100 having a base panel 102 and one or more stiffener-members 108.Accordingly, the anti-resonant panel 100 act as an interior side wallpanel that at least partially defines an enclosed cabin 155 of theaircraft 145.

The double-pane acoustic effect generally has two low-frequency resonantmodes, as shown for example in FIGS. 11A and 11B, then a rapid increasein acoustic attenuation as the frequency increases. If properlyaccounted for, the anti-resonance of the anti-resonant panel 100 and thedouble-pane effect can work together to extend the overall acoustictransmission loss through the anti-resonant panel 100 into the enclosedstructure (e.g., enclosed cabin 155 of FIG. 14). FIGS. 11A and 11Billustrate exemplary double-pane effects caused by two structures (e.g.,fuselage skin 137 and anti-resonant panel 100) resonating in phase witheach other (FIG. 11A) and out of phase with each other (FIG. 11B).

Referring to FIG. 12, in some embodiments, a method 1100 is provided formaking an anti-resonant panel 100 having a base panel 102 with a basepanel core material 104 and two base panel face sheets 106, 107. Each ofthe two base panel face sheets 106, 107 are adjacent to an opposite sideof the base panel core material 104. The method 1100 includes attachingat least one stiffener-member 108 to a base panel 102 (step 1110). Asdescribed above, the stiffener-member 108 is disposed along the basepanel 102 in a defined area 110 of the base panel 102, and the basepanel 102 includes a base panel core material 104 and two base panelface sheets 106, 107. The stiffener-member 108 includes astiffener-member core material 114 and two stiffener-member face sheets116, 117. The stiffener-member 108 is configured to provideanti-resonant performance to the base panel 102. In some embodiments,attaching the stiffener-member 108 to the base panel 102 may includecomposite layup, hot-pressing, vacuum-forming, vacuum bagging, vacuumassisted resin transfer molding (VARTM), or a combination thereof (step1112). In some embodiments, attaching the stiffener-member 108 to thebase panel 102 may include incorporating at least one of an attachmentmechanism 146 comprising a screw, adhesive, adhesive film, rivet, or acombination thereof to attach the stiffener-member 108 to the base panel102 (step 1114).

FIG. 12 illustrates an exemplary method 1100 of providing noiseinsulation to a structure (e.g., a fuselage skin 137) in accordance withsome example embodiments described herein. In particular, method 1100 isillustrated which includes attaching at least one stiffener-member 108to the base panel 102 (step 1110) (see e.g., FIGS. 2A-2G, 4A-4C, 5A and5B and the description related to each provided herein). The method 1100may also include providing a base panel 102 comprising a base panel corematerial 104 and two base panel face sheets 106, 107 (step 1108) (seee.g., FIGS. 6A-6D). As described above, attaching the stiffener-member108 to the base panel 102 may include composite layup, hot-pressing,vacuum-forming, vacuum bagging, VARTM, and combinations thereof (step1112). Attaching the stiffener-member 108 to the base panel 102 mayinclude incorporating at least one attachment mechanism 146 including ascrew, adhesive, adhesive film, rivet, or combinations thereof to attachthe stiffener-member 108 to the base panel 102, as shown in step 1114.Various embodiments as disclosed herein may be incorporated into methodsof providing noise insulation.

In some embodiments, the method 1100 may include removing an interiorportion 148 of the stiffener-member 108 creating a hollowed portion 124in the stiffener-member 108 prior to attaching at least onestiffener-member 108 to the base panel 102 (step 1109).

FIG. 13 is a flow chart for an exemplary method 1200 of forming ananti-resonant panel 100 in accordance with some example embodimentsdescribed herein. In particular, method 1200 includes forming astiffener-member 108 configured to provide anti-resonant performance toa base panel 102 by disposing at least one stiffener-member face sheets116 and/or 117 over a stiffener-member core material 114 (step 1210) andattaching the stiffener-member 108 to a defined area 110 of the basepanel 102 (step 1220). Various embodiments as disclosed herein may beincorporated into methods of providing noise insulation.

Referring again to FIGS. 9A and 9B, FIGS. 10A and 10B, and FIGS. 11A and11B, in some embodiments, a system 200 may be provided that includes astructure 136 (e.g., fuselage skin 137) and at least one anti-resonantpanel 100 adjacent the structure (e.g., fuselage skin 137). Thestructure 136 (e.g., fuselage skin 137) defines an exterior section 138a and an interior section 138 b and may form an enclosed cabin 155. Thestructure 136 (e.g., fuselage skin 137) is adjacent to the anti-resonantpanel 100 and may work in conjunction with the anti-resonant panel 100to provide improved noise-insulation (see e.g., grounding members 134discussed with regards to FIGS. 10A and 10B and/or double pane effectdiscussed with regards to FIGS. 11A and 11B). In some embodiments, theanti-resonant panel 100 is used in an aircraft (e.g., aircraft 145),where the aircraft is the system 200 having the anti-resonant panel 100.

FIG. 14 provides exemplary areas where the anti-resonant panels 100 maybe used on an aircraft 145 and provides an example of anti-resonantpanels 100 incorporated with the fuselage skin 137 of the aircraft 145forming an enclosed cabin 155. The anti-resonant panels 100 may be addedto the aircraft 145 as an addition or substitution where the trim panels154 are located. For instance, the stiffener-members 108 may beincorporated onto a base panel 102, which enables broadbandsound-blocking performance of the anti-resonant panel 100. FIG. 14provides one example of the application of the stiffener-members 108;however, the stiffener-members 108 may be added to various locationsthroughout the enclosed cabin 155. As shown in FIG. 14, theincorporation of the stiffener-members 108 to the base panels 102provides improved sound blocking as compared to the base panel 102alone. Sound waves 109 are reflected off the anti-resonant panels 100.The anti-resonant panels 100 thereby provide improved noise blocking forthe enclosed cabin 155, particularly at low frequencies.

In some embodiments, noise insulation may be provided to an enclosedcabin 155. Noise insulation may be provided to an enclosed cabin 155 bypositioning at least one anti-resonant panel 100 adjacent to theenclosed cabin 155, the at least one anti-resonant panel 100 comprisinga base panel 102 and at least one stiffener-member 108 attached to thebase panel 102, wherein the at least one stiffener-member 108 providesanti-resonant performance to the base panel 102 to reduce noisepropagation into the enclosed cabin 155. In some embodiments,positioning at least one anti-resonant panel 100 adjacent to theenclosed cabin 155 includes positioning the anti-resonant panel 100 aspreviously described adjacent the enclosed cabin 155. In someembodiments, the at least one anti-resonant panel 100 may be coupled tothe enclosed cabin 155. In some embodiments, the at least oneanti-resonant panel 100 may be coupled to the enclosed cabin 155 usinggrounding members 134.

An example of effective anti-resonant performance is depicted in FIG.15. In particular, FIG. 15 illustrates an exemplary prediction using thefinite element analysis (FEA) method and experimentally measuredresults. The performance shown in FIG. 15 is merely representative andis relative to the noise that may be blocked. The performance shown inFIG. 15 is not intended to limit the present disclosure. FIG. 15 showsthe insertion loss performance of an anti-resonant panel 100 (solidline), along with the matched FEA prediction (depicted as diamonds). Thedashed curve is the equivalent mass law prediction using an identicalmass density of an isotropic plate. As shown in FIG. 15, theanti-resonant panel 100 may provide improved noise blocking,particularly at relatively low frequencies, and much higher noiseblocking than seen with an equivalent mass density. As shown in FIG. 15,in this embodiment, the equivalent mass to achieve the shown loss innoise is about sixteen (16) times that used in the anti-resonant panel100. Other degrees of improvement may be possible.

FIG. 16 illustrates an effect of adding exemplary inertial members 126to an anti-resonant panel 100 to enable a wider bandwidth ofanti-resonant performance in an exemplary embodiment. As shown in FIG.16, in some embodiments, the addition of the inertial members 126 (shownby squares) may provide a wider bandwidth of anti-resonant performancecompared to an embodiment without the inertial member 126 (shown bytriangles). In some embodiments, the addition of the inertial members126 may reduce dips in anti-resonant performance seen in embodimentswithout the inertial members 126. The inertial members 126 generallyhelp tune the acoustic performance of the anti-resonant panel 100,providing a wider bandwidth of anti-resonant performance. The inertialmembers 126 may define a new acoustic boundary 132 point, line, or area,and may enable the creation of a better-defined anti-resonant panel 100.The inertial members 126 may help move the resonance frequencies awayfrom the target frequency range.

FIG. 17 illustrates how the anti-resonance and double pane effects mayadd together to attenuate a very large acoustic frequency band gap. Inparticular, FIG. 17 illustrates an exemplary predicted transmission lossperformance comparison using the double-pane effect between theuntreated trim panels (dashed curve) (including a base panel 102 andgrounding members 134) and anti-resonant trim panels (triangle marks)(including a base panel 102, grounding members 134, andstiffener-members 108). For instance, as shown in this embodiment, thelow-frequency transmission-loss performance may increase, and any dipsin the transmission loss may shift to a higher frequency therebyproviding improved noise insulation for lower frequencies.

FIG. 18 depicts exemplary shapes of stiffener-members 1800 foranti-resonate panels 100 in an illustrative embodiment. The shapesillustrated for stiffener-members 1800 in FIG. 18 are not all inclusive,and stiffener-members 1800 have other shapes in other embodiments.

In this embodiment, stiffener-members 1800 comprise an AdditivelyManufactured (AM) component formed from aircraft-rated materials, suchas Nylon (e.g., Nylon 12). The use of an AM process for fabricatingstiffener-members 1800 allows stiffener-members 1800 to be formed into avariety of shapes quickly and efficiently, thereby providing a technicalbenefit during noise mitigation testing. Further, the use of an AMprocess for stiffener-members 1800 allows stiffener-members 1800 to beformed to have a variety of dimensions, thereby providing a technicalbenefit during noise mitigation testing. Generally, stiffener-members1800 operate similarly to stiffener-members 108 to provide anti-resonateperformance to base panels 102, as previously described. Thus thepreviously described benefits, capabilities, and performance of usingstiffener-members 108 for anti-resonant panels 100 applies equally touse of stiffener-members 1800 for anti-resonant panels 100.

In one non-limiting example, stiffener-members 1800 are formed usingSelective Laser Sintering (SLS). SLS is an AM technique that uses alaser as the power source to sinter powdered material together to form asolid structure. SLS involves the use of a high-power laser (forexample, a carbon dioxide laser) to fuse small particles of plastic,metal, ceramic, or glass powders into a mass that has a desiredthree-dimensional shape. The laser selectively fuses powdered materialby scanning cross-sections generated from a 3-D digital description ofthe part (for example from a CAD file or scan data) on the surface of apowder bed. After each cross-section is scanned, the powder bed islowered by one layer thickness, a new layer of material is applied ontop, and the process is repeated until the part is completed.

SLS has many benefits over traditional manufacturing techniques. Theability to quickly produce a unique part is the most obvious because nospecial tooling is required and the parts can be built in a matter ofhours. Since the components are built layer by layer, it is possible todesign internal features and passages that could not be cast orotherwise machined. Complex geometries and assemblies with multiplecomponents can be simplified to a single component. Further, since SLSdoes not require special tooling like castings, it is convenient forshort production runs.

Referring again to FIG. 18, five exemplary shapes of stiffener-members1800 are illustrated. In particular, FIG. 18 illustratesstiffener-member 1800-1, stiffener-member 1800-2, stiffener-member1800-3, stiffener-member 1800-4, and stiffener-member 1800-5. In thisembodiment, stiffener-member 1800-2 and stiffener-member 1800-3 aremirror images of each other, and stiffener-member 1800-4 andstiffener-member 1800-5 are also mirror images of each other. Althoughnot illustrated in FIG. 18, stiffener-members 1800 comprise astiffener-member core and a stiffener-member face sheet that form aseamless single component part. As stiffener-members 1800 in thisembodiment are formed from an AM process, both the stiffener-member coreand the stiffener-member face sheet are formed layer-by-layer using aseries of manufacturing steps.

FIG. 19 is a block diagram of anti-resonant panel 100 utilizingstiffener-member 1800 in an illustrative embodiment. In this embodiment,stiffener-member 1800 includes a stiffener-member core 1902 having a topsurface 1904, a bottom surface 1906, and a plurality of cells 1908formed from walls 1910 that extend from top surface 1904 to bottomsurface 1906. In one embodiment, cells 1908 comprise hexagonal cellsformed from walls 1910. In another embodiment, cells 1908 are surroundedby a perimeter wall 1912.

In this embodiment, stiffener-member 1800 further includes astiffener-member face sheet 1914 formed onto top surface 1904 ofstiffener-member core 1902 as a continuous structure 1916. Becausestiffener-member core 1902 and stiffener-member face sheet 1912 ofstiffener-member 1800 are formed as continuous structure 1916,discontinuities do not exist between top surface 1904 ofstiffener-member core 1902 and stiffener-member face sheet 1914. Forexample, during an AM process used to form stiffener-member 1800, afirst series of manufacturing steps are used to form stiffener-membercore 1902, and a second series of the manufacturing steps are used toform stiffener-member face sheet 1914 on top surface 1904 ofstiffener-member core 1902 to form continuous structure 1916. In onenon-limiting example, SLS is used to selectively sinter multiple layersof a material (e.g., Nylon) together during the AM process to form bothstiffener-member core 1902 and stiffener-member face sheet 1914 ascontinuous structure 1916.

As described previously, attachment mechanism 146 (e.g., an adhesive) isused to mechanically attach stiffener-member 1800 to base panel 102. Inthis embodiment, attachment mechanism 146 attaches bottom surface 1906of stiffener-member core 1902 to base panel face sheet 106 of base panel102. In some embodiments, attachment mechanism 146 comprises bondingbottom surface 1906 of stiffener-member core 1902 to base panel facesheet 106 using an adhesive.

FIG. 20 depicts exemplary configurations of stiffener-members 1800 in ananti-resonant panel 100 employed as aircraft cabin panel 202 in anillustrative embodiment. In this embodiment, stiffener-members 1800-1are proximate to ends 2002-2003 of aircraft cabin panel 202, eachincluding variable height features to enable stiffener-members 1800-1 toclear support beams (not shown). These variable height features will bediscussed later. Further in this embodiment, stiffener-member 1800-2 andstiffener-member 1800-3 are proximate to end 2002 of aircraft cabinpanel 202, with stiffener-member 1800-3 proximate to side 2004 ofaircraft cabin panel 202 and stiffener-member 1800-2 proximate to side2005 of aircraft cabin panel 202. Stiffener-member 1800-4 andstiffener-member 1800-5 are proximate to end 2003 of aircraft cabinpanel 202, with stiffener-member 1800-5 proximate to side 2004 andstiffener-member 1800-4 proximate to side 2005.

FIG. 21 illustrates a transmission loss graph of a mass-law predictionand experimentally measured results in an illustrative embodiment. Theperformance shown in FIG. 21 is merely representative and is relative tothe noise that may be blocked. The performance shown in FIG. 21 is notintended to limit the present disclosure. FIG. 21 shows the transmissionloss performance of an anti-resonant panel 100 employed as aircraftcabin panel 202, along with the mass-law prediction. Line 2104represents the mass-law prediction when aircraft cabin panel 202 isblank. Line 2104 represents the mass-law prediction when aircraft cabinpanel 202 includes stiffener-member 1800-3 and stiffener-member 1800-5.Line 2102 represents the mass-law prediction when aircraft cabin panel202 includes stiffener-member 1800-2, stiffener-member 1800-3,stiffener-member 1800-4, and stiffener-member 1800-5.

Line 2107 represents the experimentally measured results when aircraftcabin panel 202 is blank, line 2106 represents the experimentallymeasured results when aircraft cabin panel 202 includes stiffener-member1800-3 and stiffener-member 1800-5, and line 2105 represents theexperimentally measured results when aircraft cabin panel 202 includesstiffener-member 1800-2, stiffener-member 1800-3, stiffener-member1800-4, and stiffener-member 1800-5. As shown in FIG. 21, anti-resonantpanel 100 employed as aircraft cabin panel 202 provides improved noiseblocking, particularly at low frequencies, and a higher noise blockingthan found with an equivalent mass density.

FIG. 22 is an isometric view of stiffener-member 1800-3 in anillustrative embodiment. In this view, stiffener-member face sheet 1914has been removed to reveal stiffener-member core 1902, which comprises aplurality of cells 1908 having walls 1910 that extend from top surface1904 of stiffener-member core 1902 to bottom surface 1906 ofstiffener-member core 1902. In this embodiment, cells 1908 are in theshape of a hexagon, although cells 1908 have other shapes in otherembodiments.

In this embodiment, cells 1908 are surrounded by perimeter wall 1912. Insome embodiments, stiffener-member core 1902 has a height 2202 between0.5 inches and 1 inch, with a preferred height of 0.75 inches. In thisembodiment, perimeter wall 1912 has a thickness 2204 of between 0.075and 0.125 inches, with a preferred thickness of 0.1 inches. Further inthis embodiment, walls 1910 of cells 1908 have a thickness 2206 between0.1 and 0.2 inches, with a preferred thickness of 0.15 inches.

FIG. 23 is an isometric view of stiffener-member 1800-3 in anillustrative embodiment. In this view, stiffener-member 1800-3 includesstiffener-member face sheet 1914, which obscures stiffener-member core1902. In this embodiment, stiffener-member face sheet 1914 has athickness 2302 between 0.15 inches and 0.25 inches, with a preferredthickness of 0.2 inches.

In some embodiments, stiffener-members 1800 may have areas that includestiffener-member core 1902 along with areas that have a differentconstruction. This is illustrated in FIG. 24, which is an isometric viewof stiffener-member 1800-1 in accordance with some example embodimentsdescribed herein. In FIG. 24, stiffener-member 1800-1 includes a pad2402, which provides a clearance between structural supports proximateto aircraft side panel 202 and stiffener-member 1800-1. In someembodiments, pad 2402 is a solid material (e.g., Nylon).

In this embodiment, pad 2402 has a height 2402 of between 0.15 inchesand 0.25 inches, with a preferred height of 0.2 inches. Pad 2402 has awidth 2206 that varies based on the dimensions of the structuralsupports that are proximate to aircraft side panel 202.

FIG. 25 is a flow chart of a method 2500 of making an anti-resonantpanel in an illustrative embodiment. Method 2500 will be described withrespect to stiffener-member 1800 of FIG. 19, although method 2500applies equally to other configurations of stiffener-member 1800.

Step 2502 of method 2500 comprises attaching at least onestiffener-member 1800 along base panel 102 in a defined area of basepanel 102, where the defined area is less than a full area of base panel102. To do so, bottom surface 1906 of stiffener-member core 1902 isattached to base panel face sheet 106 of base panel 102, usingattachment mechanism 146.

FIG. 26 is a flow chart of a method 2600 of making an anti-resonantpanel in another illustrative embodiment. Method 2600 will be describedwith respect to stiffener-member 1800 of FIG. 18, although method 2600applies equally to other configurations of stiffener-member 1800. Thesteps of method 2600 are not all inclusive, and method 2600 may includeother steps, not shown. Further, the steps may be performed in analternate order.

Using an AM process comprising a first series of manufacturing steps(e.g., SLS), stiffener-member core 1902 (see FIG. 19) is formed havingtop surface 1904, bottom surface 1906, and cells 1908 having walls 1910that extend from top surface 1904 to bottom surface 1906 (see step2602). For instance, stiffener-member core 1902 may be built uplayer-by-layer from bottom surface 1906 to top surface 1904, with walls1910 of cells 1908 formed concurrently. In some embodiments, perimeterwall 1912 is also formed concurrently. See, for example, FIG. 22.

In response to forming stiffener-member 1902, the AM process continuesthrough a second series of manufacturing steps to form stiffener-memberface sheet 1914 on top surface 1904 of stiffener-member core 1902. Forinstance, stiffener-member face sheet 1914 may be built uplayer-by-layer until a desired thickness is achieved forstiffener-member face sheet 1914 (e.g., thickness 2302 ofstiffener-member 1800-3 of FIG. 23).

In response to forming stiffener-member face sheet 1914 on top surface1904 of stiffener-member core 1902, bottom surface 1906 ofstiffener-member core 1902 is attached to a defined area of base panel102, where the defined area is less than a full area of base panel 102(see step 2606).

The use of stiffener-members 1800 on base panel 102 providesanti-resonant performance to base panel 102, while adding negligibleweight to base panel 102. Further, fabricating stiffener-members 1800using an AM process enables a variety of shapes, dimensions, andmaterials to be quickly tested for their performance characteristics inproviding anti-resonant capabilities to base panel 102.

The word “exemplary”, when used herein, is intended to mean “serving asan example, instance, or illustration”. Any implementation describedherein as “exemplary” is not necessarily preferred or advantageous overother implementations.

As used in the specification and in the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly indicates otherwise. For example, reference to “astiffener-member” includes a plurality of such stiffener-members, unlessthe context clearly indicates otherwise.

As used in the specification and in the appended claims, reference to“on” includes both embodiments in which a component is disposed directlyon another component as well as embodiments in which one or moreintervening layers or elements are disposed between the components.

Many modifications and other embodiments of the disclosures set forthherein will come to mind to one skilled in the art to which thesedisclosures pertain having the benefit of teachings presented in theforegoing descriptions and the associated drawings. Although the figuresonly show certain components of the apparatus and systems describedherein, it is understood that various other components may be used inconjunction with the supply management system. Therefore, it is to beunderstood that the disclosures are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Moreover, the steps in the method described above may not necessarilyoccur in the order depicted in the accompanying diagrams, and in somecases one or more of the steps depicted may occur substantiallysimultaneously, or additional steps may be involved. Although specificterms are employed herein, they are used in a generic and descriptivesense only and not for purposes of limitation.

What is claimed is:
 1. An anti-resonate panel, comprising: a base panelcomprising a base panel core material and two base panel face sheets,each of the two base panel face sheets adjacent to an opposite side ofthe base panel core material; and at least one stiffener-memberpositioned along the base panel in a defined area of the base panel, thedefined area being less than a full area of the base panel, wherein theat least one stiffener-member comprises a stiffener-member core having atop surface, a bottom surface in contact with the base panel, aplurality of cells having walls that extend from the top surface to thebottom surface, and a stiffener-member face sheet that is seamlesslyintegrated with the walls of the plurality of cells along the topsurface.
 2. The anti-resonant panel of claim 1, wherein: the at leastone stiffener-member is configured to provide anti-resonant performanceto the base panel by adding stiffness to the defined area of the basepanel at a low mass density.
 3. The anti-resonant panel of claim 1,wherein: the at least one stiffener-member comprises two or morestiffener-members, each positioned along the base panel in respectivedefined areas of the base panel.
 4. The anti-resonant panel according toclaim 1, wherein: the stiffener-member core and the stiffener-memberface sheet comprises Nylon.
 5. The anti-resonant panel of claim 1,wherein: the cells comprise hexagonal cells.
 6. The anti-resonant panelof claim 1, wherein: the stiffener-member core includes a perimeter wallextending from the top surface to the bottom surface that surrounds theplurality of cells and is seamlessly integrated with the walls of thecells that are in contact with the perimeter wall.
 7. The anti-resonantpanel of claim 1, wherein: the anti-resonant panel is configured toreduce noise propagation through the anti-resonant panel at frequenciesbetween 300 Hertz to 1000 Hertz.
 8. The anti-resonant panel of claim 1,wherein: the bottom surface of the at least one stiffener-member isbonded to the base panel utilizing an adhesive.
 9. A method of making ananti-resonant panel having a base panel with a base panel core materialand two base panel face sheets, each of the two base panel face sheetsadjacent to an opposite side of the base panel core material, the methodcomprising: attaching at least one stiffener-member along the base panelin a defined area of the base panel, the defined area less than a fullarea of the base panel, the at least one stiffener-member including astiffener-member core having a top surface, a bottom surface in contactwith the base panel, a plurality of cells having walls that extend fromthe top surface to the bottom surface, and a stiffener-member face sheetthat is seamlessly integrated with the walls of the plurality of cellsalong the top surface.
 10. The method of claim 9, wherein: the at leastone stiffener-member is configured to provide anti-resonant performanceto the base panel by adding stiffness to the defined area of the basepanel at a low mass density.
 11. The method of claim 9, whereinattaching the at least one stiffener-member comprises: attaching two ormore stiffener-members, each positioned along the base panel inrespective defined areas of the base panel.
 12. The method of claim 9,wherein: the cells comprise hexagonal cells.
 13. The method of claim 9,wherein: the stiffener-member core includes a perimeter wall extendingfrom the top surface to the bottom surface that surrounds the pluralityof cells and is seamlessly integrated with the walls of the cells thatare in contact with the perimeter wall.
 14. The method of claim 9,wherein: the anti-resonant panel is configured to reduce noisepropagation through the anti-resonant panel at frequencies between 300Hertz to 1000 Hertz.
 15. The method of claim 9, wherein attaching the atleast one stiffener-member comprises: bonding the bottom surface of theat least one stiffener-member to the base panel utilizing an adhesive.16. A method of making an anti-resonant panel having a base panel with abase panel core material and two base panel face sheets, each of the twobase panel face sheets adjacent to an opposite side of the base panelcore material, the method comprising: additively forming, using a firstseries of manufacturing steps, a stiffener-member core having a topsurface, a bottom surface, and a plurality of cells having walls thatextend from the top surface to the bottom surface; additively forming,using a second series of the manufacturing steps, a stiffener-memberface sheet on the top surface of the stiffener-member core; andattaching the bottom surface of the stiffener-member core to a definedarea of the base panel, wherein the defined area of the base panel isless than a full area of the base panel.
 17. The method of claim 16,wherein: the manufacturing steps comprise Selective Laser Sintering(SLS).
 18. The method of claim 17, wherein: the stiffener-member coreand the stiffener-member face sheet comprise Nylon.
 19. The method ofclaim 16, wherein: the cells comprise hexagonal cells.
 20. The method ofclaim 16, further comprising: additively forming, using the first seriesof manufacturing steps, a perimeter wall extending from the top surfaceto the bottom surface that surrounds the plurality of cells and isseamlessly integrated with the walls of the cells that are in contactwith the perimeter wall.